Its basic approach is to
combine a theoretical effort in the energetics and dynamics
of chemical reactions with an experimental effort in dynamics
and kinetics under chemically isolated conditions and also
under more complex conditions in flames.contributions concerning the dynamics of chemical elementary processes.
This program studies elementary chemical reactions, related
non-reactive energy transfer processes, and coupled kinetics
processes involved in combustion. Its basic approach is to
combine a theoretical effort in the energetics and dynamics
of chemical reactions with an experimental effort in dynamics
and kinetics under chemically isolated conditions and also
under more complex conditions in flames.
The theoretical effort, involving five staff members, embraces both large-scale applications of existing theoretical methods and the development of new methods that efficiently exploit advanced computer architectures. Both electronic structure techniques that determine intermolecular forces and dynamics techniques that determine molecular responses to these forces will be pursued.
Simulations of more complex combustion environments involving coupling kinetics are also being pursued. The experimental effort, involving five staff members, encompasses state-resolved measurements in flow tubes at low temperatures, thermal reaction kinetics measurements in shock tubes at high tempertatures, photoionization measurements of thresholds and state-resolved product distributions, and in situ X-ray scattering measurements of sooting flames. Reaction rates, branching ratios (between different neutral products or between ionic and neutral products),
product distributions, the effect of initial vibrational excitation on reactivity, ion-cycles for thermochemical information, and the morphology and chemistry of soot formation can all be examined. The close coupling between theory and experiment brings a unique combination of expertise to bear on the study of chemical reactivity.
This work is designed to provide a fundamental understanding of both major and trace reactions of importance in combustion.
Many of the projects of our group involve several group members and a mixture of expertise that complicates any attempt to organize our projects by authors or by categories. Nonetheless, in the sections that follow, each of our ten staff will describe their contribution to the group's achievements. To give a flavor of the group's accomplishments, I cite here several illustrative achievements:
Our group initiated and led a theoretical/experimental multi-national-laboratory collaboration that definitively showed that the heat of formation of the OH radical has been overestimated in all standard thermochemical tables by approximately 0.5 kcal/mol.
Our group has concluded by systematic experimental measurements and supportive theoretical calculations that the recombination rate of H+O2 is an order of magnitude faster in water vapor than in other common buffer gases (e.g., rare gases, oxygen, nitrogen, or methane) because of long-range polar-polar electrostatic interactions.
Our group, in collaboration with theoretical and experimental programs at other DOE laboratories, has demonstrated that the addition-elimination process CH3+O ® H2+HCO with a barrier but no saddle point
and no steepest descent reaction path can still account for ~20% of the reaction branching ratio. This is the first documentation of a reaction that can not be modeled by reaction paths.
Utilizing state-of-the-art wave packet propagation techniques, the role of excited state and non-adiabatic dynamics in the O(1D) + H2 ® OH + H reaction was investigated. Extensive calculations, including the ground and two excited electronic states predicted the ratio of the reactive cross sections for rotationally excited and cold H2. The results disagreed with earlier experiments and motivated a new molecular beam experiment that agreed quantitatively with the theoretical predictions.
Our group has developed new ways to investigate the long-time dynamics of nonlinear master equations. This has allowed us to develop rate laws to describe association kinetics and vibrational relaxation. Applications have been made to methyl recombination and the nonlinear vibrational relaxation of oxirane. In both cases, our rate laws model the process correctly while standard rate laws break down when reactant concentrations within inert buffer gases become a few percent or higher.
Our group, in collaboration with computational scientists in the Mathematics and Computer Science Division, has developed a new general way to iteratively solve matrix eigenvalue problems. The method, called SPAM, uses projection operators and a simple matrix that approximates the exact one to accelerate the Davidson iterative method (typically used in electronic structure calculations). The method is general to all eigenvalue problems where physical insight can produce a simple approximate matrix.
Our group, in collaboration with the Carbon Chemistry group within the division, has initiated a program of in situ analysis of nano-scale soot within flames using small angle X-ray scattering (SAXS) at the Advanced Photon Source. This effort, one of the first SAXS applications in the gas-phase, has discovered detailed structure in soot distributions in laminar flames and has led to development of a prototype detector to monitor transient (e.g., droplet) flames with a time resolution of ~10 µs. Such a detector will be useful in many other areas of chemistry. Our group has carried out one of the most detailed state- to-state studies ever performed of vibrational autoionization in a polyatomic molecule, in this case ammonia.
Of all the fundamental or combination normal mode excitations tried, initial excitation of the umbrella mode is found to be the most effective in promoting autoionization and the final products of the process involve a change in either electronic symmetry or rotational quantum number depending on the specific autoionizing level.
These accomplishments and others in the research summaries to follow illustrate that our group has increasingly reached out beyond group boundaries to carry out fundamental studies in chemical reactivity.
We have always had strong experimental-theoretical interactions within the group and an active collaboration with university programs. However, in the last several years we have collaborated more intimately than before with other parts of the national laboratory system. For example, our involvement with the Carbon Chemistry group within our division is expected to be a long-term collaboration driven by a mutual interest in soot chemistry and a complementary background in experimental and theoretical expertise.
Likewise, our involvement with computational scientists in other divisions is also long-term and a recognition of the fact that computational chemistry worldwide is one of the leading consumers of computer hardware resources and both a beneficiary and a source of advanced computer software. Our involvement with other national laboratories, especially the Combustion Research Facility at Sandia National Laboratory and the Environmental Molecular Science Laboratory at Pacific Northwest National Laboratory, reflects the complementary expertise that has become centered at those laboratories. The broader involvement by the group has not only furthered our combustion research program but has also won additional funding outside of Chemical Sciences.
This additional funding includes discretionary (LDRD) funding for the soot studies and Scientific Discovery through Advanced Computing (SciDAC) funding from the Mathematics, Information, and Computer Science (MICS) office in DOE.
While different funding sources do not have identical missions, we believe the additional funding we receive will only augment and accelerate the Chemical Sciences supported program in fundamental combustion research.
In the future, our group intends to continue to pursue experimental and theoretical studies into the details of chemical reactivity manifested in combustion. We feel this is the "golden age" of combustion research in which effective coupling of experiment and theory can be achieved for increasingly complex chemical reactions that are prevalent but still poorly characterized within combustion. However,
the increasing complexity of reactions we are studying and the broader collaborations the group has become involved in suggests future group interests not exclusively tied to gas-phase processes that have been our focus in the past. For example, the soot project will involve us in cluster and agglomeration kinetics that has both gas phase and gas-surface overtones.
Furthermore, the experimental and theoretical techniques we develop for soot studies may well be applicable to studies of complex systems outside of combustion, such as molecular self-assembly or chelation kinetics. Another example of a broader study of chemical reactivity our group is involved in is a new collaboration with university researchers into reaction kinetics under carbon nanotube confinement.
While all these activities are rooted in our experience and expertise in gas phase combustion research, the research itself is leading the group to a future in which broader issues of chemical reactivity can be addressed beyond the context of combustion but within the fundamental research agenda of Chemical Sciences.
Yuan Tseh Lee was born on November 19, 1936 in Hsinchu, Taiwan.
His father is an accomplished artist and his mother a school teacher.
He started his early education while Taiwan was under Japanese occupation - a result of a war between China and Japan in 1894. His elementary education was disrupted soon after it started during World War II while the city populace was relocated to the mountains to avoid the daily bombing by the Allies. It was not until after the war when Taiwan was returned to China that he was able to attend school normally as a third year student in grade school.
His elementary and secondary education in Hsinchu was rather colorful and full of fun. In elementary school, he was the second baseman on the school's baseball team as well as a member of the ping-pong team which won the little league championship in Taiwan. In high school he played on the tennis team besides playing trombone in the marching band.
Besides his interest in sports during this time, he was also an avid and serious reader of a wide variety of books covering science, literature, and social science. The biography of Madame Curie made a strong impact on him at a young age. It was Madame Curie's beautiful life as a wonderful human being, her dedication toward science, her selflessness, idealism that made him decide to be a scientist.
In 1955, with his excellent academic performance in high school, Lee was admitted to the National Taiwan University without having to take the entrance examination, a practice the Universities took to admit the best students. By the end of his freshman year he had decided chemistry was to be his chosen field. Although the facilities in the Taiwan University were less than ideal, the free and exciting atmosphere, the dedication of some professors, and the camaraderie among fellow students in a way made up for it. He worked under Professor Hua-sheng Cheng on his B.S. thesis which was on the separation of Sr and Ba using the paper electrophoresis method.
After graduation in 1959, he went on to the National Tsinghua University to do his graduate work. He received his Master's degree on the studies of the natural radioisotopes contained in Hukutolite, a mineral of hot spring sediment under Professor H. Hamaguchi's guidance. After receiving his M.S. he stayed on at Tsinghua University as a research assistant of Professor C.H. Wong and carried out the x-ray structure determination of tricyclopentadienyl samarium.
He entered the University of California at Berkeley as a graduate student in 1962. He worked under the late Professor Bruce Mahan for his thesis research on chemiionization processes of electronically excited alkali atoms. During his graduate student years, he developed an interest in ion-molecule reactions and the dynamics of molecular scattering, especially the crossed molecular beam studies of reaction dynamics.
Upon receiving his Ph.D. degree in 1965, he stayed on in Mahan's group and started to work on ion molecule reactive scattering experiments with Ron Gentry using ion beam techniques measuring energy and angular distributions. In a period of about a year he learned the art of designing and constructing a very powerful scattering apparatus and carried out successful experiments on N2+ + H2 --> N2H+ + H and obtained a complete product distribution contour map, a remarkable accomplishment at that time.
In February 1967, he joined Professor Dudley Herschbach at Harvard University as a post-doctoral fellow. He spent half his time working with Robert Gordon on the reactions of hydrogen atoms and diatomic alkali molecules and the other half of his time on the construction of a universal crossed molecular beams apparatus with Doug McDonald and Pierre LeBreton. Time was certainly ripe to move the crossed molecular beams method beyond the alkali age. With tremendous effort and valuable assistance from the machine shop foreman, George Pisiello, the machine was completed in ten months and the first successful non alkali neutral beam experiment on Cl + Br2 --> BrCl + Br was carried out in late 1967.
He accepted the position as an assistant professor in the Department of Chemistry and the James Franck Institute of the University of Chicago in October 1968. There he started an illustrious academic career. His further development as a creative scientist and his construction of a new generation state-of-the-art crossed molecular beams apparatus enabled him to carry out numerous exciting and pioneering experiments with his students. He was promoted to associate professor in October 1971 and professor in January 1973.
In 1974, he returned to Berkeley as professor of chemistry and principal investigator at the Lawrence Berkeley Laboratory of the University of California. He became an American citizen the same year.
In the ensuing years, his scientific efforts blossomed and the scope expanded. His world leading laboratory now contains seven very sophisticated molecular beams apparati which were specially designed to pursue problems associated with reaction dynamics, photochemical processes, and molecular spectroscopy. His laboratory has always attracted bright scientists from all over the world and they always seem to enjoy working together. He takes great pride in the fact that more than fifteen of his former associates are serving as professors in major universities, and many others are making great contributions at the national laboratories and in the private sector.
Lee and his wife, Bernice Wu, whom he first met in elementary school have two sons, Ted (born in 1963), Sidney (born in 1966) and a daughter, Charlotte (born in 1969).